The invention relates to a hydraulic support element for a variable valve train of an internal combustion engine, which comprises a cylindrical pot-shaped housing and a hollow cylindrical piston that is guided so that it can move axially in this housing and whose inner end is supported by a compression spring on the base wall of the housing, whose outer end tops the outer edge of the housing and is constructed as a hemispherical bearing head, and whose interior is divided into an inner supply pressure space and an outer switching pressure space, wherein the supply pressure space can be connected by inlet openings in the cylindrical side walls of the housing and the piston to a cylinder head side supply pressure line and can be connected by a non-return valve to a high-pressure space surrounded between the inner end of the piston and the base wall of the housing, and in which the switching pressure space can be connected by inlet openings in the cylindrical side walls of the housing and the piston with a cylinder head side switching pressure line and by a central hole formed in the bearing head to a rocker arm side switching pressure channel.
Hydraulic support elements are used in valve trains of internal combustion engines in which the gas exchange valves, such as intake and outlet valves, are actuated by the cam of a camshaft by rocker arms. The rocker arms are connected at one end to the outer end of the valve shaft of at least one gas exchange valve and are supported on the cylinder head so that they can pivot at the other end on the same side by means of a hydraulic support element. Between its two ends, the rocker arms each contact at least one cam of a camshaft on the side facing away from the gas exchange valve and the support element. When the camshaft rotates, the rocker arms are pivoted according to the stroke contour of the cam about the bearing on the corresponding support element in the direction toward the gas exchange valve or under the effect of the valve springs in the opposite direction, whereby the relevant gas exchange valves are opened or closed.
In the hydraulic support elements there is an integrated device for the automatic equalization of a possibly present valve lash between the allocated cams of the camshaft and the valve shaft of the allocated gas exchange valve. When the support element is loaded, its piston is pressed axially into the housing of the support element, whereby a high pressure is established in the high-pressure space, by which the non-return valve is held closed and a rigid connection between the piston and the housing is formed in connection with the incompressible engine oil located in the high-pressure space. When the load is removed from the support element, its piston is pressed by the compression spring axially out of the housing and in this way an empty clearance in the valve train is compensated. Here, in the high-pressure space, a vacuum pressure is set, by which the non-return valve is opened, so that engine oil can flow out of the supply pressure space into the high-pressure space for equalizing leakage losses.
In the installed state, each support element is typically inserted into an essentially vertically aligned supporting hole of a cylinder head of the internal combustion engine. A supply pressure line of a supply oil gallery opens axially on the inside into the respective supporting hole. The supply storage space of the piston is thus in connection with this cylinder head side supply pressure line via the axially inner inlet openings in the cylindrical side walls of the housing and the piston, so that engine oil escaping from the high-pressure space due to leakage can be replaced from the supply pressure space.
In the present case, the internal combustion engine has a variable valve train in which valve strokes can be shut down or shifted by hydraulically switchable rocker arms. For transferring the engine oil that acts as a switching oil and is alternately essentially not pressurized or under a high switching pressure depending on the current switching state, a switching pressure line of a switching oil gallery opens axially farther outside in the respective supporting hole. The switching pressure space of the piston is thus connected on one side via the axial outer inlet openings in the cylindrical side walls of the piston and the housing to this cylinder head side switching pressure line and on the other side via a central bore in the bearing head of the piston to a switching pressure channel arranged in the associated rocker arm. Because the engine oil located in the supply pressure space and the engine oil located in the switching pressure space of a hydraulic support element fulfill different functions and can have different pressure values, these pressure spaces located within the interior of the piston are usually separated from each other by a partition element. A known construction of a dual-flow hydraulic support element is described, for example, in DE 103 30 510 A1.
Typically, both the supply oil gallery and also the switching oil gallery are connected to an oil supply system of the internal combustion engine, in which there is also at least one filter element for separating harmful particles, such as oil carbon particles due to combustion as well as metal particles due to work and wear. Nevertheless, harmful particles can still enter the hydraulic support elements via the supply oil gallery and the switching oil gallery, whereby both the function of the valve lash compensation in the support elements and also the switching function in the rocker arms can be negatively affected. This relates especially to the initial commissioning of the internal combustion engine after its assembly, in which particles that have not been removed from the mechanical work on the cylinder head can enter the hydraulic support elements via the supply oil gallery and the switching oil gallery and also from these elements into the switchable rocker arms. For preventing the associated disadvantages, hydraulic support elements with installed filter elements have already been proposed.
From RU 2 231 650 C2, a single-flow hydraulic support element for a non-switchable valve train of an internal combustion engine is known, in which a filter element is arranged within the piston between two diagonally opposite inlet openings arranged in the cylindrical side wall of the piston and the non-return valve. The filter element is formed of a coupling-like arched filter screen and a ring-shaped edge connector and is fixed axially in the piston by fastening element inserted into the inlet opening. Due to its ends extending from the inlet openings of the piston and engaging in an inner ring-shaped recess in the cylindrical side wall of the housing, the fastening element of the filter element is also effective as transport protection. The assembly of the filter element within the piston, however, is relatively complicated.
In FR 2 910 529 A3, a single-flow hydraulic support element for a non-switchable valve train of an internal combustion engine is described, in which a filter element constructed as a ring filter is arranged in a first arrangement in an outer ring-shaped recess and in a second arrangement on an inner ring-shaped section in the cylindrical side wall of the housing. The ring-shaped recess and the ring-shaped section are constructed in the cylindrical side wall of the housing such that the ring filter covers the respective inlet openings of the housing. The ring filter has a closed construction on the circumferential side and consists of a cylindrical filter screen and two ring-shaped edge connectors, whereby for the assembly of the filter element, strong elongation of the ring filter is required at least in the first arrangement.
In FIG. 2, DE 10 2014 033 500 A1 shows a tappet for loading a tappet rod with an oil supply via the latter “from above.” In the supply space of its pressure piston, a filter cap is attached to a bottom side of a contact for the tappet rod.